Rigid-Flexible Substrate Tapered Junction Design
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Solution Overview
Problem
Existing rigid-flexible substrates face issues with cracking, peeling, or breaking at the junction between the rigid and flexible portions due to mismatched properties and difficulties in accurate polishing, leading to increased manufacturing costs and reduced flexibility in component mounting.
Innovation Solution
A rigid-flexible substrate design featuring a tapered portion on the second resin sheet near the flexible portion, where the thickness decreases to zero at the junction, and thermocompression bonding of thermoplastic resin sheets with the same material for both portions, enhancing the boundary's smoothness and flex resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a rigid-flexible substrate is fabricated by laminating thermoplastic resin sheets with different numbers of layers for rigid and flexible portions, then the substrate achieves both rigidity and flexibility, but cracks, peel-off, or breaking occurs at the junction between rigid and flexible portions
Solution Approach 1:
The patent applies local quality by creating a tapered portion at the junction area where the number of laminated layers gradually decreases from the rigid portion toward the flexible portion. This gradual transition in structural composition at the local junction area reduces stress concentration and prevents crack initiation, while maintaining the overall rigidity-f flexibility balance of the substrate.
Solution Approach 2:
The patent implements curvature by forming a tapered portion with a gradual slope at the junction between rigid and flexible portions. This curved, tapered transition area (rather than an abrupt step) distributes mechanical stress more evenly, preventing crack propagation and peel-off at the junction while maintaining the structural integrity of both rigid and flexible areas.
2Reliability
If chamfering is performed on rigid substrate using router machining, then repeated bending strength is improved and peel-off is suppressed, but manufacturing cost increases and accuracy is difficult to achieve for downsized components
Solution Approach 1:
The patent applies self-service by designing the tapered portion to be formed automatically during the thermocompression bonding process itself, without requiring separate machining operations. The thermocompression process naturally creates the tapered transition area, making the structure self-forming and eliminating the need for additional costly and complex machining steps.
Solution Approach 2:
The patent replaces the mechanical router machining system with a thermocompression bonding system to create the tapered portion. This substitution eliminates the need for mechanical cutting tools and complex machining operations, reducing manufacturing cost and improving accuracy, especially for downsized components where router machining becomes difficult.
3Manufacturing precision
If polishing is performed on rigid-flexible substrate, then surface smoothness is improved, but it is difficult to achieve accurate polishing due to the softness of thermoplastic resin sheets
Solution Approach 1:
The patent applies preliminary action by forming the tapered portion with a smooth surface during the thermocompression bonding process itself, before any polishing operation is attempted. The thermocompression process pre-smooths the surface of the tapered portion, eliminating or reducing the need for subsequent polishing operations and avoiding the difficulties associated with polishing soft thermoplastic resin sheets.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design prevents cracking, breaking, or peeling-off of conductor wires at the boundary, improves rupture strength, and reduces manufacturing costs by ensuring a smooth boundary without special machining, while maintaining identical material properties for the rigid and flexible portions.
Implementation Method 1
thermocompression bonding of thermoplastic resin sheets with the same material for both portions
Data Source
AI summary
A rigid-flexible substrate includes a plurality of rigid portions, and a flexible portion connecting the plurality of rigid portions and including a portion of a first resin sheet including at least one layer of a thermoplastic resin sheet, the rigid portions including a portion of the first resin sheet other than the flexible portion, and a second resin sheet including a plurality of thermoplastic resin sheets laminated on one surface or both surfaces of the portion of the first resin sheet other than the flexible portion, and a tapered portion is provided at an end edge of the second resin sheet on a side close to the flexible portion, and a thickness of the tapered portion in a direction in which the second resin sheet is laminated decreases toward the flexible portion and is substantially 0 at a position in contact with the flexible portion.